The American Academy of Pediatrics warns that some energy drinks contain up to 500 mg of caffeine.The Post-Standard

A recent report linking energy drinks to five deaths has left caffeine lovers wondering how much of their favorite beverage is too much.

According to The Associated Press, the U.S. Food and Drug Administration is investigating reports that Monster Energy Drink, a 24-ounce beverage that contains 240 milligrams of caffeine, could be responsible for five deaths and one non-fatal heart attack dating back as far as 2004. The investigation comes just one week after the parents of 14-year-old Anais Fournier filed a wrongful death suit against Monster claiming their daughter died after drinking two of the company's energy drinks in 24 hours.

An autopsy concluded that Fournier died of cardiac arrhythmia due to caffeine toxicity, The Associated Press said. The medical examiner said she had an inherited disorder that can weaken blood vessels.

Fournier's parents claim Monster failed to warn about the risks of drinking its products.

Monster Beverage Corp. has denied that its products caused any deaths, but experts like Cleveland Clinic cardiac surgeon Dr. Marc Gillinov aren't so sure. Gillinov told CBS News that consuming large amounts of caffeine can lead to caffeine toxicity, which can lead to irritability, hyper aroused states, abnormal heart beat and cardiac arrest.

"Just think about what coffee does and multiply it by 10," he said of the symptoms.

CBS News reports that caffeine starts to become dangerous when you consume more than 1 gram of the substance and it can be lethal at 10 grams. Therefore, Gillinov recommends that people don't consume more than 400 to 500 milligrams per day. The average cup of coffee has about 100 milligrams of caffeine, though a cup of Starbucks coffee contains 260 milligrams of caffeine.

"Higher doses [of Caffeine] in the range of 250-500 mg can lead to feelings of nervousness, insomnia, mild tremors, or generalized restlessness," said Dr. Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York. "At even higher doses, caffeine can cause a hyperadrenergic syndrome that can lead to significantly elevated blood pressure as well as cardiac arrhythmias, and potentially seizures."

Because caffeine can have harmful effects on kids' developing neurological and cardiovascular systems, the American Academy of Pediatrics says that energy drinks are never appropriate for children or adolescents.

"Some cans or bottles of energy drinks can have more than 500 mg of caffeine, which is the equivalent of 14 cans of soda," warned AAP study co-author Dr. Marcie Beth Schneider.